Debt and Other Obligations Schedule of Extinguishment of Long Term Debt (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Extinguishment of Debt [Line Items]
Write-off of deferred financing costs and discounts		$ 3
Gain (Loss) on Extinguishment of Debt		(71)	$ (4)
January 2010 Tower Revenue Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount		1,250
Repayments of Debt	[1]	1,318
Gain (Loss) on Extinguishment of Debt	[2]	$ (71)

[1] Exclusive of accrued interest.

[2] Inclusive of $3 million related to the write off of deferred financing costs.